It should first be noted that each type of vehicle has a body which is symmetrically designed with respect to a datum plane which is used to establish the unique longitudinal, lateral and vertical dimensions for each vehicle. The manufacturers provide data holes in the frame of the vehicle which are used to provide the correct location of the datum points with respect to the longitudinal center line of the frame. A data sheet is developed for each type of frame for each model of an automobile. In the event of an accident, a portion of the frame may be deformed, moving one or more of the datum points in one or more directions longitudinally, laterally or vertically, thus destroying the symmetry of the vehicle.
Each of the data sheets for a particular model vehicle is provided with two zero lines, one near the front and one near the back of the auto. If the damage occurs in the front of the vehicle, the zero line in the back is used as a reference line. If the damage is in the back of the vehicle, the zero line in the front of the vehicle is used as the reference point. There are normally two datum points on the zero line. Depending on the location of the damage, the main beam is initially positioned under the vehicle and two vertical attachments are mounted on one of the bridge cross slides at the datum point positions for the zero line noted on the data sheet. The bridge is then raised to move the vertical attachments into engagement with the datum points on the zero line. A third and generally fourth vertical attachment is mounted on another cross slide in a position to engage third and fourth datum points on the vehicle. The cross slide is then moved to align the third and fourth vertical attachments with the third and fourth datum points. The measuring bridge is then located in the center of the vehicle and establishes a datum plane parallel with the bottom of the vehicle.
After orienting the measuring bridge under the vehicle, additional vertical attachments are mounted on the cross slides at the datum points indicated on the data sheet to determine the deviation of the damaged or deformed portions of the frame. A system as described above is available under the trade name P-188 Universal Measuring System and manufactured by the assignee of the present invention.
The P-188 measuring system is generally provided with two fixed slide arms and 2-4 independent slide arms, each of which is affixed to the center beam for longitudinal movement with respect to the center beam. Because of their fixed relationship with the center beam, it often becomes necessary to readjust the slide arms because of interference with the anchoring clamps which are attached to the vehicle. Whenever this occurs, the measuring bridge must be completely removed from the vehicle, the slide arms rearranged as required, and the measuring bridge realigned with the vehicle. Since time is essential in the cost of repairing a vehicle, the additional time required to reset the bridge increases the overall cost of the repair.